A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a driver to a destination through a calculated route. Such a navigation system detects the position of the user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Typically, the navigation system displays a map image on a monitor screen while superimposing thereon a mark representing the current location of the user. At an intersection, the navigation system notifies the user which direction to turn at the intersection.
In creating the map data for a navigation system, geographic data available in the market is used as the original data to be converted to a map data format that is suitable for a navigation system. For example, such geographic data is in a GDF (geographic data file) format which is a standardized format for geographic (map) data that is typically provided by a map data provider. The GDF format defines the data structure (physical record structure) which includes “Field Name”, “Size”, “Type”, “Description”, etc. in a predetermined order.
Since the GDF is created as a map data file to simply describe the topological structures, it is not always well suited for a navigation system unique to a particular manufacturer of the navigation systems. Thus, a manufacturer usually converts the GDF format data into a data format that is more suitable for the hardware and software of a proprietary navigation system. Further, to improve the functionality of the navigation system, it is frequently necessary for the manufacture of the navigation system to modify, remove and add a relatively large amount of data to the original map data file.
Since the GDF format file has disadvantages that it is difficult to modify its data contents, in the conventional technology, the GDF format is converted to a file format, for example, PSF (physical storage format), to actually use the map data in a navigation system. The PSF is a format that takes the limitation imposed by the hardware performance of the navigation system into consideration while making the map data suitable for performances of the navigation system.
FIG. 1 is a schematic diagram showing an example as to how the original GDF map data is constructed into meshed data in the PSF file. In this method, a map area 63 is a graphical representation of a selected area such as a county, a city, etc., that is generated by the original map data provided by a map data provider. In the PSF file, the map area 63 is divided into a plurality of meshed portions (cells) 61 each having a rectangular shape of a predetermined size. Each meshed portion 61 includes bit-mapped graphical data (raster graphics) for displaying a map image on a display screen of the navigation system.
During the process of converting the GDF map data to the PSF map data, in order to accommodate several different map scales for enlarging or shrinking the map image on the display screen, a plurality of bitmap data with different sizes need to be produced based on the GDF map data. This requires additional processes of data conversion and calculation, which increases the conversion time and labor. Further, because the map area is divided into a plurality of meshed portions 61, the chances of causing inconsistencies between adjacent meshed portions 61 would increase, which is undesirable since the accuracy of the map would be deteriorated. Moreover, because the format of the PSF map data is fundamentally different from that of the GDF map data, the process to convert the GDF map data into the PSF map data is extremely complex and time consuming. For example, in the case where the map data covers a large area such as the whole north America, the process for conversion can take several weeks.
Other disadvantage associated with the PSF map data in the conventional technology is its inflexibility and lack of expandability. As noted above, it is often necessary to update the map data for a navigation system because of new roads and new buildings. The process of adding the new data or modifying the existing data in the PSF data file generally requires regeneration of all the map data. It may also be necessary to change the compilation (conversion) program. This is partly due to the fundamental difference between the PSF data format and GDF data format, since the PSF data utilizes raster graphic data even though the GDF format data utilizes a text based format. In addition, because the PSF data is machine dependent, recompilation of the data would be necessary if different hardware or software is to be used or an existing navigation system is changed or modified.
As described above, the conventional technology utilizing the conversion between the GDF format and the PSF format involves various disadvantages. Since it is always necessary that the old map data be updated or supplemented by new map data for a navigation system, there is a need of a new flexible format for map data that can be easily understandable and editable. Further, there is a need of a new map data format for a navigation system that can be quickly converted from the GDF format data.